Winch for towing submerged objects

ABSTRACT

A winch makes it possible for a fish fitted with sonar to be towed behind a boat. The winch includes a sensor for measuring the attitude of the fish and a device for controlling, using this measurement, a servo cylinder actuator which alters the inclination of the jib to keep this attitude constant. The winch makes it possible to reduce jerks in the tensile stress applied to the cable which tows the fish.

TECHNICAL FIELD

The present invention relates to winches which make it possible to towbehind a towing structure, such as an oceanographic ship, a submergedobject such as a "fish" containing, for example, sonar for mapping thesea bed.

BACKGROUND ART

It is known to tow, at the end of a cable, behind a boat, a submergedbody called a fish because of its resemblance to this animal. Outsidethese periods of use, the fish is brought back on board the boat bywinding up the towing cable on a winch. To facilitate handling, thecable passes over an idling pulley located at one end of an armarticulated at its other end to the boat, in such a way that, byrotating about this articulation, the arm passes from an extendedposition, in which the pulley hangs out over the sea, to a raisedposition, in which it hangs out over the deck of the boat. The arm alsoincludes, at this pulley, a device forming a cradle on which the fishcomes to rest after it has been raised.

On account of the equipment on board the fish, the latter can reach aconsiderable mass, of the order of several tones. Since the towingstructure moves along only at a relatively low speed, on the order ofabout ten knots at most, in particular so as not to impose too high atensile stress on the towing cable, the vertical distance of separationof the fish from the boat is relatively small and the angle between thisvertical and the straight line which joins to the boat to the fish istypically on the order of 30°.

Moreover, on account of the stresses which it has to withstand, thetraction cable is itself large and heavy. Because of this, it is notpossible to neglect its weight in relation to that of the fish and itfurthermore is subjected to significant drag. What is more, it exhibitssignificant deflection in relation to the straight line joining the fishto the boat.

Under the effect of the waves, the boat displays random movements whichare passed on to the cable and to the fish. Because of the aboveeffects, the movement of the fish does not reproduce that of the boatand it is therefore not possible, during the processing of the sonarsignals for example, to compensate for the movements of the fish simplyby taking into account the movements of the boat. What is more, thestresses in the cable due to these movements are absolutely excessiveand it is necessary to minimize them as far as possible.

A known solution to this problem consists supporting the arm with theaid of a cylinder actuator connected to a pneumatic accumulator, so thatthe arm oscillates about its point of articulation on the boat so thatthe head of the arm follows a substantially rectilinear path at anapproximately constant speed. As may be easily imagined, this result isobtained only very approximately with such a passive system. Inaddition, on account of the masses and stiffnesses involved, the naturalfrequency of this assembly is, in most cases, relatively close to thatof the swell, which leads resonance phenomena liable to increase thestresses applied to the cable.

DISCLOSURE OF THE INVENTION

To mitigate these drawbacks, the invention provides a winch for towingsubmerged objects, comprising a jib having a base which can pivot on asubstantially horizontal pin and a head fitted with an idling pulley forsupport a towing cable, main means for keeping this jib raised inrelation to horizontal at an angle of inclination α which can vary aboutan average value α₀ allowing the towing operations, mainly characterizedin that it furthermore includes means for causing the inclination of thejib to vary about α₀ so as to limit the variations in the tensile stressin the cable.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the invention will appear clearly inthe following description given by way of example which is non-limitingand made with reference to the appended figures wherein:

FIG. 1 is a schematic diagram of a winch according to the invention;

FIG. 2 is a variant of FIG. 1;

FIG. 3 is a diagram of the forces as a function of the angle of FIG. 1;

FIG. 4 shows a simplified plan view of this winch; and

FIG. 5 shows a hydraulic circuit for controlling the cylinder actuators.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 shows the arm 100 of the winch, which is comparable to the jib ofa crane, and which supports the cable for towing the fish. This jib 100is articulated at one end by means of a pin 101 on a frame, not shown,which is itself fixed to the deck of the towing structure. The drum 102of the winch, which contains the towing cable 103, rotates about thispin 101. This cable 103 is unreeled from the drum 102, turns around anidling pulley 104 located at the other end of the jib 100 and then goesdown. When the cable is unwound, it therefore extends into the sea totow the fish 117 therein.

A load cylinder actuator 105 connected to a hydraulic accumulator 116,fixed on the one hand to the support frame of the winch and on the otherhand to the jib 100, allows the latter to be supported and allows it tobe caused to pivot about the pin 101 so that this jib makes an angle αwith the horizontal.

When the fish is to be raised, it is placed in a cradle, not shown,located at the end of the jib 100 beneath the pulley 104, and thecylinder actuator 105 allows, with the aid of pumping-up means, notshown, the arm to be lifted so as to bring the fish up again above thedeck of the structure, the angle α then having a rather large value.Once the fish has been raised above the water, it is brought above thedeck of the boat, either by rotating the jib in the horizontal sense orby a backwards translational movement of the latter.

On the other hand, when the cable 103 has been unwound to tow the fishbelow the water astern of the structure, the cylinder actuator 105lowers the jib so as to place the end of the latter carrying the pulley104 above the surface of the water, in order to have a correctdeflection of the cable 103 in relation to the stern of the boat. Theangle α is then relatively small.

Under these towing conditions, and as a function of the relativemovements of the boat, of the surface of the sea and of the fish, thejib 100 tends to oscillate about the pin 101 under the effect of thevariations in the tensile stress which are due to these movements. Infact, the stresses go back to the load cylinder actuator 105 which,being for example of the hydraulic type, tends to oscillate under theaction of these stresses around the equilibrium point which has beenfixed by the means for pumping up the cylinder actuator.

As was mentioned earlier, the elastic assembly formed by all theseelements, and especially by the jib and the load cylinder actuator, doesnot allow the tensile stresses imposed on the cable 103 by theserelative movements to be damped correctly.

According to the invention, a servo cylinder actuator 106, which isconnected to a servovalve 107 supplied by a pump 108, has been arrangedin parallel with the load cylinder actuator 105. A electronic controldevice 109 allows the servovalve 107 to be controlled so as to supplythe servo cylinder actuator 106 via two supply hoses 110 and 111. Inthis manner, the cylinder actuator 106 thrusts the jib upwards or pullsit downwards so as to keep a substantially constant tensile stress inthe cable 103, and also so as to keep a substantially constant height atthe end of the jib.

Various parameters may be used to control the servovalve 107 by means ofthe control device 109.

According to the invention, sensors 118 are used which are located inthe fish 117 and which measure the attitude of this fish. The signalscoming from these sensors are applied to the control box 109 via aconnection shown separately in the figure, but which in practice passesvia the towing cable 103, in an arrangement known in the art. Indeed itis even pointless in general to provide specific transmission means andsensors as these already exist and are normally used to correct theinformation from the apparatuses, sonar for example, contained in thefish. It therefore suffices to extract, from the exploitation memberslocated in the boat, the signals corresponding to the attitude angle ofthe fish and to apply them to the box 109.

This box operates in an open-loop mode by applying signals to theservovalve 107 which tend to bring the attitude of the fish back to 0.If the attitude increases, the cylinder actuator is supplied in onedirection and if it decreases it is supplied in the other. The box 109is therefore equivalent to a differential amplifier. As this systemoperates in open-loop mode, it is possible to use a relatively high gainwithout too great a risk of oscillation, at the very least to somedegree. In fact, there is indeed a feedback, which is mechanical, viathe intervention of the tension in the cable itself. The mass of thecable/fish assembly and the elasticity of this cable are therebyautomatically taken into account in the control, and the results areexcellent.

In practice, it is found that above a certain value of the gain of thecontrol 109, an oscillation having a frequency of a few Hz, for example5 Hz, is obtained. It then suffices to bring the gain back to a valueslightly below this limiting value to be steady in all circumstances,even in rough seas, at the very least for cable lengths below 50 m.Above this, the oscillations reappear because of the increase in theelasticity and in the mass. To reduce the oscillations, the gain isdivided by 2 between 100 and 150 m, and then by 3 above that. Indeed, alength is finally reached such that the elasticity damps out by itselfthe movements of the swell, such that the device is no longer necessary.

To compensate for drift, in the amplifier for example, it is possible tointroduce into the control signal a correction signal coming, forexample, from a potentiometer 115 giving the position of the jib, with arelatively low gain, to prevent the jib from hitting a limit stop.

According to one variant of the invention, it is possible to use, asshown in FIG. 2, an accelerometric sensor 112 fixed to the end of thejib supporting the pulley 104. This sensor is arranged so as to measuresubstantially the vertical component of the acceleration. To do this,various arrangements can be used, the simplest of which consists inusing an accelerometer sensitive along a single axis and fixed to theend of the jib so that this axis is substantially vertical for theposition of the jib corresponding to the standard towing conditions. Ithas been possible to show that this arrangement was sufficient tominimize the jerks on the cable correctly as the latter can withstandreasonable stress variations and it is therefore pointless to obtain aperfect system which would be extremely difficult to produce.

The signals coming from the accelerometer 112 are therefore applied tothe control device 109 in which they undergo processing which allowscontrol signals to be applied to the servovalve 107 to supply thecylinder actuator 106 in such a way that the vertical acceleration atthe head of the jib is minimal. The electronic control box 109implements a servo-controlled procedure very similar to those known inthe current art. The procedure used consists, for example of a doubleintegration leading to positional control of the jib or of a singleintegration leading to control of the speed, the parameters of thesecontrols allowing the instantaneous value of the acceleration to beminimised.

The implementation of this procedure and of its variant uses, in thecontrol box, either standard-type analogic circuits or, preferably,digital circuits, such as a microprocessor suitably programmed forimplementing the procedure.

As has been emphasized, it is neither useful nor necessary to have aperfect device, and under these conditions, some drift is observed whichis, in any case, inevitable in the case of the variant, even with themost accurate devices since at least one integration is performed usingthe value of the acceleration. To limit the effects of this drift, twodetectors 113 and 114, of the end-of-travel type for example, are usedwhich are placed on either side of the jib at positions corresponding tothe maximum permissible deflection, for example ±5° about the set-pointvalue of the angle α. These devices are connected to the control box 109and, when the jib actuates one of them, this devices emits a signalwhich is detected in this control box, which leads to a correction ofthe signal applied to the servovalve so as to return the jib slowly tothe correct value of the angle α. An angle sensor 115 can also be used.In this case, the correction is carried out by a long integration onthis angle sensor.

The diagram of FIG. 3 shows the total force F applied to the jib as afunction of the angle α-α₀, α₀ being the average value which wouldcorrespond to an absence of movement of the boat. α₁ and α₂ are the twolimit-stop values corresponding to the two end-of-travel devices 113 and114.

If the cylinder actuator 105 alone were supplied by a servovalvecontrolled by the electronic circuits, the value of the force applied bythis load cylinder actuator 105 would vary about an average value F₀with extreme values F₁ and F₂ corresponding to α₁ and α₂. The work to beprovided by the pump for supplying this cylinder actuator wouldtherefore be proportional to the obliquely hatched area, which isconsiderable.

According to the invention, by using an auxiliary servo cylinderactuator 106, the force applied by the load cylinder actuator 105remains permanently substantially equal to F₀, whereas the force exertedby the servo cylinder actuator 106 varies between F₁ -F₀ and F₀ -F₂since this force sometimes reinforces and sometimes counteracts theaction of the load cylinder actuator. Under these conditions, the workdeveloped by the pump 108 is therefore equal to the vertically-hatchedarea which is much smaller than the previous one.

Therefore, by using a servo cylinder actuator which is placed parallelwith the load cylinder actuator, it is possible to use a pump having apower which is much less than if the load cylinder actuator were to besupplied directly. As a consequence, the size of the other hydraulicmembers (servovalve, hoses, etc.) is reduced.

The mounting of the two cylinder actuators shown in FIG. 1 on the sameside of the jib with the two thrust shafts joined together correspondsto an explanatory purpose.

To facilitate the construction of the device, a mounting is preferablyused such as shown diagrammatically in FIG. 4 which corresponds to aplan view of the elements of FIG. 1.

As is seen, the jib 100 of the crane is in the form of a triangle whosebase is fixed to the pin 101 and whose apex receives the pulley 104.This triangle is formed by two arms.

The load cylinder actuator 105 is fixed to one of the two arms and theservo cylinder actuator 106 to the other. On account of the sizes to beused for the components forming the crane, because of the permanenttensile stress to be withstood, there is no risk of theobliquely-applied stresses occasioned by this arrangement leading tooperational difficulties or to distortions of the assembly.

In an embodiment variant shown diagrammatically in FIG. 5, which hasbeen limited to the members which are useful in understanding thevariant, not only is the cylinder actuator 106 supplied by theservovalve 107 but also the cylinder actuator 105. This cylinderactuator 105 comprises, completely normally, a first chamber 301 locatedon the other side of the thrust shaft 302 in relation to a piston 308and supplied by a pressurized tank 303 which allows a substantiallyconstant force F₀ to be obtained with the cylinder actuator 105irrespective of the extent to which the rod 302 is pushed in.

The cylinder actuator 105 furthermore comprises, on the thrust rod side,a second chamber 304 which is itself supplied by the servovalve 107 soas to counteract the effect of the pressure exerted in the chamber 301.What is more, the servovalve 107 supplies the cylinder actuator 106 soas to reinforce the action of the cylinder actuator 105.

The supply of the cylinder actuator 106 can be carried out in twodifferent ways:

in a first case, in which the cylinder actuators 105 and 106 aredifferent, a cylinder actuator 106 smaller than the cylinder actuator105 is used so that the chamber 305, located on the other side of thethrust rod 306 in relation to the piston 309 of this cylinder actuator,has a cross-sectional surface area equal to that of the chamber 304,taking into account the size of the thrust rod 302;

in a second case, two identical cylinder actuators are used and, for thecylinder actuator 106, both the chamber 305 and the chamber 307 whichlies on the thrust rod 306 side are supplied. The thrust obtained withthe cylinder actuator 106 then corresponds to the difference in theforces exerted on the two faces of the piston 309, which are notidentical since the cross-section of the rod 306 is to be subtractedfrom the surface-area of the piston on the chamber 307 side. In orderfor the thrusts for servo-controlling the cylinder actuators 105 and 106to be equal, these cylinder actuators, identical to each other, are thenchosen in such a way that the cross-section of the rods 302 and 306 isequal to the free surface-area of the pistons 308 and 309 on thechambers 304 and 307 side.

Cylinder actuators also exist commercially which include, in a singlecylinder, two pistons fixed to the same single thrust rod. The pistonlocated at the end of the rod delimits, in the cylinder, a main thrustchamber connected to the accumulator. The piston located on the roddelimits, in interaction with an intermediate partition which is fixedto the inner wall of the cylinder and in which the rod slides, twoservo-control chambers connected to the servovalve. It is thus possibleto use a single cylinder actuator for fulfilling the two functions.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

I claim:
 1. A winch for towing submerged objects with a towing cable,which comprises:a jib having a drum, a substantially horizontal pinabout which the drum rotates and an idling pulley connected to the jibto support the towing cable, main means for keeping said jib raised inrelation to horizontal at an angle of inclination α which is variableabout an average value α₀ for allowing towing operation, and means forcausing the inclination of the jib to vary about average value α₀ so asto limit the variations in the tensile stress in the cable, wherein themeans for causing the inclination of the jib to vary comprises means formeasuring the attitude of a submerged object towed by the winch, andcontrol means for relieving and counteracting stresses developed by themain means for keeping the jib substantially at the angle α in order tokeep this attitude at a substantially constant value.
 2. Winch accordingto claim 1, wherein the constant value corresponds to the horizontal. 3.Winch according to claim 1 or 2, which comprises means for adjusting thegain of the control means to just below the threshold for oscillation ofthe assembly.
 4. Winch according to claim 3, wherein the gain isadjusted as a function of a length dimension of the towing cable. 5.Winch according to any one of claims 1 or 2, which comprises a loadingcylinder actuator for supporting the jib with a substantially constantforce and a servo cylinder actuator supplied by a servovalue forapplying, to the jib, a variable force which is added to or subtractedfrom the force exerted by the main cylinder actuator.
 6. Winch accordingto claims 1 or 2, which comprises limit stops for detecting maximum andminimum values α₁ and α₂ of the inclination of the jib and for actuatingthe control means so as to reestablish the inclination angle α₀. 7.Winch according to claims 1 or 2, which comprises an angle sensor fordetecting maximum and minimum values α₁ and α₂ of the inclination of thejib and for actuating the control means so as to establish the averageinclination angle α₀.
 8. A winch for towing submerged objects with atowing cable, which comprises:a jib having a drum, a substantiallyhorizontal pin about which the drum rotates and an idling pulleyconnected to the jib to support the towing cable, a main mechanism forkeeping said jib raised in relation to horizontal at an angle ofinclination α which is variable about an average value α₀ for allowingtowing operation, and a mechanism for causing the inclination of the jibto vary about average value α₀ so as to limit the variations in thetensile stress in the cable, wherein the mechanism for causing theinclination of the jib to vary comprises a mechanism for measuring theattitude of a submerged object towed by the winch, and a controlmechanism for relieving and counteracting stresses developed by the mainmechanism for keeping the jib substantially at the angle α in order tokeep this attitude at a substantially constant value.
 9. Winch accordingto claim 8, wherein the constant value corresponds to the horizontal.10. Winch according to claims 8 or 9, which comprises a mechanism foradjusting the gain of the control mechanism to just below the thresholdfor oscillation of the assembly.
 11. Winch according to claim 10,wherein the gain is adjusted as a function of a length dimension of thetowing cable.
 12. Winch according to any one of claims 8 or 9, whichcomprises a loading cylinder actuator for supporting the jib with asubstantially constant force and a servo cylinder actuator supplied by aservovalue for applying, to the jib, a variable force which is added toor subtracted from the force exerted by the main cylinder actuator. 13.Winch according to claims 8 or 9, which comprises limit stops fordetecting maximum and minimum values α₁ and α₂ of the inclination of thejib and for actuating the control mechanism so as to reestablish theinclination angle α₀.
 14. Winch according to claims 8 or 9, whichcomprises an angle sensor for detecting maximum and minimum values α₁and α₂ of the inclination of the jib and for actuating the controlmechanism so as to establish the average inclination angle α₀.